A wide range of sealing systems have been developed for weapons having stacked projectile arrangements or barrel assemblies, such as the “wedging” systems described in WO 94/20809 and WO 97/04281, and the “projectile-to-projectile” sealing arrangements which in WO 03/089871, for example. The projectiles in these weapons are generally caseless and temporary seals are therefore required to prevent blow-back of ignition gases down the barrel. If no sealing system is present, hot pressurised gases from ignition of a leading projectile in a stack will usually cause uncontrolled ignition of the propellant in a trailing projectile.
Wedging systems generally form seals by interaction between successive projectiles in a stack. An axial force down the barrel causes the interaction either when the stack is loaded in a barrel or when projectiles are fired from the barrel, or both. The interaction causes a collar or tail on each projectile to expand into tight contact with the bore of the barrel, preventing blow-back past that point. Depending on the pressures involved, the expanding part of each projectile is typically a soft metal or plastic which deforms into a circumferential contact with the barrel. Various “forward”, “reverse”, “nose-to-tail” and “stick” systems have been developed.
Weapons that use wedging systems can be difficult for a user in the field to reload and generally require loading in a factory or other specialised environment. A large force is usually required to form the seal and the surfaces that interact within the barrel must be sufficiently clean. Special tools may be required. Subsequent shocks or vibration may weaken the seals and reduce the reliability of the weapons. Long cartridges containing pre-stacked projectiles are used for reloading in the field, but when partially empty these may be problematic for the user.
Systems that utilise projectile-to-projectile sealing form seals by interaction between successive projectiles. These also are not generally suitable for reloading in the field.